1. Field of the Invention
The invention relates to an image processing apparatus and an image processing method for performing a pixel density conversion of an image and to a storage medium.
2. Related Background Art
Hitherto, what is called a color original copying apparatus as shown in FIG. 10 has been known as a system for digitally reading a color original image and generating a copy image.
In FIG. 10, reference numeral 1001 denotes an image scanner for reading an original and performing a digital signal process, and 1002 indicates a printer. An image corresponding to an original image read by the image scanner 1001 is printed and outputted onto a paper in a full color by the printer 1002. In the image scanner 1001, reference numeral 1000 denotes a mirror surface pressure plate. An original 1004 put on a copyboard glass (hereinafter, referred to as a platen) 1003 is irradiated by lamps 1005 and an obtained image is guided to mirrors 1006, 1007, and 1008. An image is formed by a lens 1009 onto a solid-state image pickup device sensor (hereinafter, referred to as CCD) 1010 of three lines. Three image signals of red (R), green (G), and blue (B) as full color information are sent to a signal process unit 1011. The lamps 1005 and mirror 1006 are mechanically moved in the direction perpendicular to the electric scanning (main-scan) direction of the line sensor at a speed v, and the mirrors 1007 and 1008 are mechanically moved in the direction perpendicular to the electric scanning (main-scan) direction of the line sensor at a speed (½)v, thereby scanning (sub-scan) the whole surface of the original. The original 1004 is read at a resolution of 600 dpi (dots/inch) in both main-scan and sub-scan.
The signal process unit 1011 electrically processes the read image signal, separates it into color components of magenta (M), cyan (C), yellow (Y), and black (Bk), and sends them to the printer 1002. A color component of one of M, C, Y, and Bk is sent to the printer 1002 with respect to one scan of the original in the image scanner 1001. One print-out operation is completed by scanning the original four times in total.
Pixel signals of M, C, Y, and Bk sent from the image scanner 1001 are transmitted to a laser driver 1012. The laser driver 1012 modulates a semiconductor laser 1013 in accordance with the transmitted image signals. A laser beam scans the surface of a photosensitive drum 1017 through a polygon mirror 1014, an f-θ lens 1015, and a mirror 1016. Image data is written at a resolution of 600 dpi (dots/inch) in both main-scan and sub-scan in a manner similar to the reading mode.
Reference numeral 1018 denotes a rotary developer comprising a magenta development unit 1019, a cyan development unit 1020, a yellow development unit 1021, and a black development unit 1022. The four development units are alternately come into contact with the photosensitive drum 1017, thereby developing an electrostatic latent image formed on the photosensitive drum by toners.
Reference numeral 1023 denotes a transfer drum. The paper which is fed from a sheet cassette 1024 or 1025 is wound around the transfer drum 1023, thereby transferring the images developed on the photosensitive drum onto the paper.
After the images of four colors of M, C, Y, and Bk were sequentially transferred as mentioned above, the paper passes through a fixing unit 1026, the toners are fixed onto the paper, and thereafter, the paper is delivered.
According to the conventional example as described above, it is fundamentally necessary that the image scanner for reading the original and the printer for outputting a copy image synchronously operate. That is, the image signals of R, G, and B read by the CCD sensor are processed every pixel by the signal process unit, converted into image signals of M, C, Y, and Bk, successively sent to the printer, and written onto the photosensitive drum by the laser beam, thereby forming the copy image.
In the conventional example, one of M, C, Y, and Bk is used for forming the image and the image forming process is repeated with respect to each color, so that the original is continuously read four times.
It is not always necessary to continuously perform the reading operation of the original four times but there is also a construction such that the image data which was read only once is stored in temporary storing means and the stored image data is read out and outputted synchronously with the image formation of each of M, C, Y, and Bk.
However, although there is no need to store the image data into the storing means in the former construction, the scanner and printer need to simultaneously operate. Therefore, for example, in the case where a heating unit of the fixing unit (in case of an ordinary thermal fixing type) of the printer is not sufficiently heated, since the printer is in a standby mode, the copying operation and the original reading operation cannot be performed.
In case of copying a plurality of copies of each of a plurality of originals, it is necessary to perform the operation for reading one original plural times in correspondence to the output of a plurality of copies. The reading operation has to be performed with respect to each of a plurality of originals. Thus, a time which the user has to expend for such a purpose is very long.
In the latter construction, the scanner and printer can perform the original reading operation asynchronously and, also in case of outputting a plurality of copies, it is sufficient to perform the original reading operation once per original. However, since an amount of image data to be stored in the storing means is extremely large, it is difficult to simultaneously store a plurality of original images. Therefore, if it is intended to read a plurality of original images in a lump and realize an exchange of pages, a synthesis output of a plurality of original images, or the like after completion of the reading operation, a storage device of a very large capacity is needed and it is not practical. It is also impossible to perform a layout synthesis by enlargement and reduction of the stored image data.
In the case where it is intended to perform the optimum process in consideration of a feature of the image data, it is necessary to detect the feature of the image. A point of making handling of the image easy and outputting the image of a high quality in case of performing the layout synthesis by the enlargement and reduction in the process using the feature data is not sufficiently examined.